Coolant for air-bag gas generator and production method therefor

ABSTRACT

The present invention provides a coolant for an air bag inflator in which unevenness in density in the axial direction is reduced even though the coolant is compressed in its axial direction. 
     The coolant is a molded product made of wire rods and compressed in its axial direction. An absolute value of a difference between a radial pressure loss of the axially upper half portion of the coolant and a radial pressure loss of the axially lower half portion of the coolant is 10 mm H 2 O or less at a flow rate of 250 liters/minute under the atmosphere of 20° C.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP00/04672 which has an Internationalfiling date of Jul. 12, 2000, which designated the United States ofAmerica.

TECHNICAL FIELD TO WHICH THE PRESENT INVENTION BELONGS

The present invention relates to a coolant for an air bag inflator and aprocess for providing the same.

RELATED ART

An air bag apparatus is mounted to a vehicle such as an automobile inorder to protect a passenger from the impact of collision. The air bagapparatus actuates an inflator when a sensor detects the impact, andform a cushion (air bag) between the passenger and the vehicle.

The inflator used for the air bag apparatus is activated by an impactsensor detecting an impact, thereby discharging an operating gas(combustion gas) for inflating the air bag (bag body). The operating gasfor inflating the air bag (bag body) is usually cooled and/or purifiedby coolant means accommodated in a housing of the inflator and then, thegas is discharged from a gas discharge port of the housing andintroduced into the air bag.

Conventionally, since the coolant means functionally needs to purify andcool the combustion gas generated due to combustion of the gasgenerating means, a molded product of wire mesh made of various wiremeshes is generally used as the coolant means. In particular, when themolded product of wire mesh is formed to have a desired size, strengthand pressure loss, preferably, a compress-molded product of wire meshobtained by compressing the molded product of wire mesh in the axialand/or radial direction is used. Such a compress-molded product of wiremesh is generally formed by putting a molded product of metal wire meshinto a mold and compressing with one-shot presswork. And EP00623373discloses a method of producing the coolant means including a process ofcompressing with the presswork. According to this method, a wire rods ofa cooling material is deformed into a waveform, then put into a mold,and lightly compressed to roughly determine its shape, thereby forming asemi-molded product. Consequently, the semi-molded product is coiledaround with wire rods deformed into a waveform and then again placedinto the mold and pressed, thereby forming the coolant means.

In the coolant means, the combustion gas generated due to combustion ofthe gas generating means should pass uniformly through the coolantmeans, and further, the need to arrange the axis-disposing direction ofthe coolants in the housing should be eliminated. In a view of theabove, it is preferable that inequable density in the axially upper andlower ends of the coolant (inequable in pressure loss in the radialdirection) is made as consistent as possible.

However, conventionally, no improvement concerning the unevenness in aradial pressure loss of the coolant has been found. Especially in thecase of the compressed molded product of wire mesh obtained bycompressing the molded product of wire mesh, mostly, the coolant meansis compressed at a stroke(s) only on one axial side. Because of thiscompression manner, the compressed side tends to shrunk more, and thedensity of the coolant means in the axial direction becomes uneven.Therefore, the radial pressure losses in the axially upper and lowerportion of the coolant cannot be uniformed.

The coolant means produced by such a conventional method has unevenpressure loss due to a difference in the density generated in the axialdirection. As a result, in the inflator using such a coolant means,output is varied due to the direction to which density of the coolantmeans is uneven (i.e., due to the difference of the pressure loss).

Disclosure of the Present Invention

Therefore, it is an object of the present invention to provide a coolantto solve the problems of the above conventional coolant means, which ismade of wire rods, compressed at least in the axial direction to have adesired size, strength and pressure loss and have a small unevenness indensity in the axial direction, and also to provide a method ofproducing the coolant. It is another object of the invention to providecoolant means which needs no disposing direction in a housing of aninflator.

A coolant means for an air bag inflator of the present invention isobtained by compressing a molded product made of wire rods at least inthe axial direction. This coolant means is characterized in that adifference between a radial pressure loss of an axially upper halfportion of the coolant and a radial pressure loss of the axially lowerhalf portion of the coolant is made as small as possible. As a result,according to the coolant means of the present invention, a combustiongas generated due to combustion of the gas generating means can passuniformly through the coolant means, and it is unnecessary to arrangethe disposing direction of the coolant in a housing.

That is, a coolant for an air bag inflator of the present invention iscylindrical in shape, disposed in a housing of the inflator for the airbag in order to cool and/or purify a gas discharged from the inflator,and obtained by compressing axially a molded product made of wire rodson the axially opposite ends. Further, in the coolant obtained bycompressing a molded product made of wire rods in the axial direction,an absolute value of a difference between a radial pressure loss of theaxially upper half portion of the coolant and a radial pressure loss ofthe axially lower half portion of the coolant is preferably 10 mmH₂O orless, and more preferably, 6 mmH₂O or less at a flow rate of 250liters/minute under the atmosphere of 20° C.

The radial pressure loss of the axially upper half portion of thecoolant is measured in such a manner that an inner surface of theaxially lower half of the coolant is covered with a covering member anda gas at a flow rate of 250 liters/minute is introduced into the coolantunder the atmosphere of 20° C. And the radial pressure loss of theaxially lower half portion of the coolant is measured in such a mannerthat an inner surface of the axially upper half of the coolant iscovered with a covering member and a gas at a flow rate of 250liters/minute is introduced into the coolant under the atmosphere of 20°C.

In a method of producing a coolant for an air bag inflator including acompressing process of compressing a cylindrical molded product in theaxial direction, by this compressing process, a difference in thepressure losses between the axially opposite ends of the coolant can be10 mmH₂O or less when it is measured in accordance with the followingmethod:

<Measuring Method>

-   -   1) an inner peripheral surface of a cylindrical coolant is        covered from its axial end to its one-half the height with a        covering member;    -   2) one end of the coolant in which the covering member is fitted        is closed with a supporting member having a manometer, the other        end of the coolant is closed with another supporting member        having a gas-inflow pipe and a gas-flow meter, and the coolant        is fixed in the axial direction so that air will not leak        between the ends of the coolant and the supporting members;    -   3) the air at 250 liters/minute is introduced from the        gas-inflow pipe into an internal space of the covering member        under the atmosphere of 20° C. and the pressure loss is        measured;    -   4) next, the coolant is turned upside down in the axial        direction, the opposite side of 1) (i.e., the side through which        the air passed in 3)) is now covered with the covering member,        and the pressure loss of the coolant is measured under the same        conditions as 2) and 3); and    -   5) a difference in the pressure loss values obtained in 3)        and 4) is obtained, and its absolute value is determined as a        difference in the pressure losses in the radial direction in the        axial ends of the coolant.

It is preferable that the coolant for an air bag inflator of the presentinvention is formed by laminating plain-knitted wire mesh having adiameter of 0.3 to 0.6 mm and then, compressing the laminated wire meshin the radial and axial directions. And it is also preferable that thecoolant has a bulk density of 3.0 to 5.0 g·cm⁻³, and more preferably 3.5to 4.5 g/cm⁻³. And preferably, the coolant has a pressure loss of 10mmH₂O to 2000 mmH₂O with respect to an amount of air of 1000 litersmin⁻¹ under the atmosphere of 20° C. Desirably, the coolant is obtainedby forming plain-knitted wire mesh made of stainless-steel wire rodsinto an annular laminated body and compressing the laminated body.

An inflator using the coolant having a small density difference in theaxial direction exhibits a stable output performance. That is, in thecase of a coolant having a difference in density in the axial direction,when a gas generated from the gas generating means passes through adenser portion in density of the coolant, a residence time of the gas inthe coolant becomes longer. Consequently, heat exchange is carried outsufficiently, which lowers a temperature of the generated gas and anoutput of the inflator in result. On the other hand, when a gas passesthrough a thinner portion in density of the coolant, a ventilationresistance of that portion is lower than that of the denser portion, theheat exchange is not carried out so effectively, which does not lower atemperature of the generated gas. In the coolant having adensity-difference in the axial direction, the output performance variesbased on the difference in the temperatures of the generated gases. Thecoolant of the present invention has a small density difference in theaxial direction and thus, the inflator using this coolant can exhibitsthe stable output performance.

When the above-described coolant is produced, a stainless steel ispreferably used and especially, SUS304, SUS310S, SUS316 (JIS Standard)can be used. SUS304 (18Cr-8Ni-0.06C) exhibits excellent corrosionresistance as austenitic stainless steel. In addition, anexpansion-suppressing means can be formed at the outer peripheralportion of the coolant. The expansion-suppressing means functions as ameans to reliably keep a gap between the coolant and the housing(especially at the time of actuation of the inflator) when the coolantis disposed in the inflator. For example, the expansion-suppressingmeans can be realized by disposing a laminated wire-mesh layer or thelike having different wire diameter, pressure loss or the like outsidethe coolant. In this case, the coolant has a double layer structure, andthe outer layer prevents the coolant from expanding, due to a gaspressure at the time of actuation of the inflator, to close the gapbetween the coolant and the housing.

The present invention also provides a method of producing a coolant foran air bag inflator including a compressing process of compressing amolded product particularly in the axial direction.

That is, the present invention provides the method of producing acoolant for an air bag inflator including a compressing process ofcompressing a cylindrical molded product at least in the axialdirection, wherein, in the compressing process, axially opposite sidesof the molded product are compressed in the axial direction. Preferably,the compressing process is carried out such that an absolute value of adifference between a radial pressure loss of the axially upper halfportion of the coolant and a radial pressure loss of the axially lowerhalf portion of the coolant is adjusted to be 10 mmH₂O or less at a flowrate of 250 liters/minute under the atmosphere of 20° C. The radialpressure loss of the axially upper half portion can be measured in sucha manner that an inner surface of the axially lower half of the coolantproduced in the above method is covered with a belt-like member and agas at a flow rate of 250 liters/minute is introduced into the inside ofthe coolant under the atmosphere of 20° C. And the radial pressure lossof the axially lower half portion of the coolant can be measured in sucha manner that an inner surface of the axially upper half of the coolantis covered with a belt-like member and a gas at a flow of 250liters/minute is introduced into the inside of the coolant under theatmosphere of 20° C. It is preferable that the compressing process iscarried out such that a difference in pressure losses between theaxially opposite ends of the coolant is adjusted to be 10 mmH₂O or lesswhen it is measured in accordance with the above-described measuringmethod.

Such a compressing process can be carried out, for example, as follows.After the molded product is compressed in the axial direction as thefirst compression step, the molded product is turned upside down in theaxial direction and then, compressed in the axial direction as thesecond compression step, or alternatively, the molded product iscompressed on the axial opposite sides without being turned upside down.In particular, in the case of compressing the molded product in twosteps, it is preferable that compressing distances of the first andsecond compression steps are substantially equal to each other. In thecompressing process, the molded product can be compressed in the radialdirection simultaneously or at different timing in addition to beingcompressed in the axial direction. In this case, a volume of a coolantcan be reduced.

The molded product used in the above producing method may be an annularlaminated body obtained by forming a plain-knitted wire mesh made ofstainless steel wire rods into a cylindrical body, and folding one endof the cylindrical body outwardly and repeatedly. Or the molded productmay be an annular laminated body obtained by forming a plain-knittedwire mesh made of stainless steel wire rods into a cylindrical body,pressing the cylindrical body in the radial direction to form a platebody, and rolling the plate body many times cylindrically. In the moldedproduct obtained in this manner, a surface of the cylindrical body comeson the end surface of the coolant, and therefore, the cut portion of thewire mesh is not outcropped on the end face of the material. Therefore,the cut portion does not hurt a hand of a user.

The above coolant or the coolant produced by the above method is used asa coolant means for an air bag inflator comprising, in a housing thereofwith a gas discharge port, an ignition means to be activated upon animpact, gas generating means which is to be ignited and burnt by theignition means for generating a combustion gas, and a coolant means forpurifying and/or cooling the combustion gas, thereby realizing an airbag inflator of the present invention. When the inflator uses thecoolant of the present invention, a stable actuating performance can beobtained irrespective of a direction of the coolant. As the membersother than the coolant means, such as known gas generating means,ignition means and the like can be used in the inflator.

The air bag inflator is accommodated in a module case together with anair bag (bag body) which introduces therein a gas generated by theinflator to inflate, thereby making an air bag apparatus. In this airbag apparatus, the inflator is actuated on an impact sensor detectingthe impact, and a combustion gas is discharged from a gas dischargingport of the housing. The combustion gas flows into the air bag torupture the module cover and expands, thereby forming cushion absorbingthe impact between a passenger and a hard structural component in thevehicle.

The coolant of the present invention is made using wire rods andcompressed at least in the axial direction to obtain a desired size,strength and pressure loss, and thereby realizing a coolant in whichunevenness in the density in the axial direction is reduced and the needof arranging a disposing direction when disposing in the housing iseliminated. And by adopting the above coolant, an air bag inflator witha stable operating output can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cylindrical wire mesh in processing toa coolant of the present invention;

FIG. 2 is a schematic view of an annular molded product formed byfolding one end of the cylindrical body outwardly and repeatedly;

FIG. 3 are schematic views showing compressing process of the coolant ofthe invention;

FIG. 4 is a schematic view of a plate body formed by pressing thecylindrical body shown in FIG. 1 in the radial direction;

FIG. 5 is a schematic view of the molded product formed by rolling theplate body into a cylindrical shape many times;

FIG. 6 is a sectional view of an essential portion showing a measuringmethod of the coolant;

FIG. 7 is a sectional view showing one embodiment of an inflator of thepresent invention;

FIG. 8 is a sectional view showing another embodiment of the inflator ofthe invention; and

FIG. 9 is a view showing a structure of an air bag apparatus of thepresent invention.

DESCRIPTION OF REFERENCE NUMERALS

-   3 housing-   4 ignition means-   5 transfer charge-   6 gas generating agent-   7 coolant-   14 initiator collar-   22 combustion chamber-   23 ignition means accommodating chamber-   31 cylindrical body-   33, 35 molded product-   34 plate body-   40 covering member-   42, 45 supporting member-   43 gas-inflow pipe

EMBODIMENTS OF THE PRESENT INVENTION

Hereinafter, embodiments of the present invention will be explainedbased on the drawings.

“Embodiment of Coolant”

A coolant for an air bag of the present invention can be produced in thefollowing manner. First, stainless steel wires having a wire diameter of0.3 to 0.6 mm are plain-knitted to form a cylindrical body 31 as shownin FIG. 1. Then, as shown in FIG. 2, one end 32 of this cylindrical body31 is folded outwardly and repeatedly to form an annular laminated bodyas a molded product 33. The number of folding operations isappropriately determined in view of a diameter of the wire, a thicknessof the coolant and the like. Next, a following compressing process isperformed. As shown in FIG. 3, the molded product 33 is put into a mold(not shown), and is compressed on one side in the axial direction as thefirst compression step (FIG. 3 a). Then, the molded product 33 is turnedupside down in the axial direction (FIG. 3 b) and is again compressed inthe axial direction as the second compression step (FIG. 3 c). In thefirst and second compression steps, the compression distances isadjusted to be substantially equal to each other. Further, such acompressing process is performed so that an absolute value of adifference between the respective radial pressure losses of the axiallyupper half and the axially lower half of the molded product 33 isadjusted to be 10 mmH₂O or less, more preferably 6 mmH₂O or less at aflow rate of 250 liters/minute under the atmosphere of 20° C. The moldedproduct 33 explained based on FIG. 2 can also be formed by other methodshown in FIGS. 4 and 5. In this method, after forming the cylindricalbody 31 shown in FIG. 1, the cylindrical body 31 is pressed in theradial direction to form a plate body 34 as shown in FIG. 4. Then, asshown in FIG. 5, the plate body 34 is cylindrically rolled over and overto be an annular laminated body as a molded product 35. This moldedproduct 35 can be compressed in the same manner as that shown in FIG. 3to form a coolant 7. A compressing process of the molded product 35 canbe performed in the same manner as shown in FIG. 3 such that, after thefirst compression step, the molded product 35 is turned upside down andthen the second compression step is performed. Alternatively, the moldedproduct 35 can be put in the mold and compressed on the axially oppositesides without turning the product upside down.

With the above-described manufacturing method, a coolant made ofcompressed wire rods with a uniform pressure loss can be obtained.Concretely, by controlling the compressing process in the above manner,can be obtained the coolant for an air bag inflator, which is made ofwire rods, formed by being compressed in the axial direction, and inwhich an absolute value of the difference between the respective radialpressure losses of the axially upper half and the axially lower half is10 mmH₂O or less at a flow rate of 250 liters/minute under theatmosphere of 20° C.

The coolant 7 formed in the above-described manner has such a shape 36that loop-like meshes in each layer are crushed, and the crushed meshesare laminated in the radial direction. Therefore, a gap structure of thecoolant becomes complicated, and the coolant exhibits an excellentscavenging function. From this point of view, it is preferable that thecoolant is adjusted so that a bulk density of the coolant becomes 3.0 to5.0 g·cm⁻³ in the above compressing process, and that the pressure lossin general becomes 10 mmH₂O to 2000 mmH₂O with respect to an amount ofair of 1000 liters/minute under the atmosphere of 20° C.

It is possible to form a coolant having a double layer structure byinserting another laminated body into the inside of the molded product33 or 35 and compressing these. The other laminated body can be formed,for example, by winding about twice the plate body 34 shown in FIG. 4made of wire mesh having a diameter of 0.5 mm as shown in FIG. 5.

EXAMPLE

Table 1 shows a result of a test of measuring a pressure loss carriedout with the above-described coolant at the flow rate of 250liters/minute. In this test, the apparatus shown in FIG. 6 is used andthe following method is adopted.

TABLE 1 Data of Pressure Loss of Coolant (mmaq) Upper Lower Differencebetween upper No. All portion portion and lower portions 1 φ60 × φ47 ×h29.5 (250 L/min) Product manufactured under the current mass-production1 7 46 23 23 2 13 38 27 11 3 16 41 31 10 4 11 38 26 12 5 13 40 27 13 613 46 24 22 Ave. 12.2 41.5 26.3 Product manufactured by the newproduction (two times compressing processes) 1 12 40 31 9 2 16 42 32 103 17 45 35 10 4 19 39 38 1 5 17 38 40 2 6 14 42 32 10 Ave. 15.8 41.034.7 2 φ58 × φ47 × h26 (250 L/min) Product manufactured under thecurrent mass-production 1 8 28 18 10 2 10 31 17 14 3 8 33 21 12 4 8 3523 12 5 9 28 23 6 6 9 35 24 11 Ave. 8.7 31.7 21.0 Product manufacturedby the new production (two times compressing processes) 1 10 28 28 0 2 628 27 1 3 10 32 28 4 4 9 29 29 0 5 10 27 23 4 6 11 28 30 2 Ave. 9.3 28.727.5the Upper portion: the upper side is pressed in the second compressionstepthe Lower portion: the lower side is pressed in the second compressionstep<Method of the Test>

1) An inner peripheral surface of the cylindrically formed coolant 7 iscovered from its axial end to one half of the height with an annularcovering member 40.

2) With the covering member 40 inserted inside, one end of the coolant 7is closed with a supporting member 42 having a manometer 41 and theother end of the coolant 7 is closed with a supporting member 45 havinga gas-inflow pipe 43 and a gas-flow meter 44. The coolant 7 is fixed inthe axial direction so that air will not leak between the ends of thecoolant 7 and the supporting members 42 and 45.

3) The air at 250 liters/minute is introduced from the gas-inflow pipe43 into the internal space of the covering member 40, and the pressureloss is measured.

4) Next, the coolant 7 is turned upside down in the axial direction, theremained portion of the coolant which has not been covered in 1) (i.e.,the portion through which the air passed in 3)) is now covered with thecovering member 40, and the pressure loss of the coolant 7 is measuredunder the same conditions as 2) and 3).

5) A difference in the pressure loss values obtained in 3) and 4) isobtained, and its absolute value is determined as a difference inpressure losses in the radial direction of the axial ends of the coolant7.

“Embodiment of Inflator”

FIG. 7 is a longitudinal sectional view of one embodiment of an inflatorfor an air bag of the present invention.

This inflator comprises a housing 3 formed by joining a diffuser shell 1having a gas discharge port and a closure shell 2 forming an inneraccommodating space together with the diffuser, and a inner cylindricalmember 13 in a substantially cylindrical shape disposed in the housingconcentrically, an ignition means accommodating chamber 23 definedinside the inner cylinder member 13, and a combustion camber 22 definedoutside the inner cylinder member 13. In the ignition meansaccommodating chamber 23, a ignition means comprising an electricignition type ignition means 4 to be activated upon the impact and antransfer charge 5 to be ignited upon the activation of the ignitionmeans for generating a flame is accommodated. And in the combustionchamber 22, a gas generating agent 6 to be ignited and burnt by theflame of the transfer charge 5 for generating a combustion gas isaccommodated, being supported by an under plate 18. The ignition means 4is fixed in an initiator collar 14 made of iron, and a skirt of theinitiator collar 14 is fixed by crimping a lower end 21 of the innercylindrical member 13. By making the initiator collar 14 of iron, theignition means can be reliably fixed in the inflator even due to a hightemperature. With this feature, even when the inflator is ignited undera high temperature, the initiator collar can sufficiently resist acombustion internal pressure without lowering its strength and canmaintain its ability and function.

The inner cylinder member 13 defining the combustion chamber 22 and theignition means accommodating chamber 23 is provided with aflame-transferring hole 26 closed by a seal tape 27. Since the seal tape27 is ruptured by a flame of the transfer charge 5, the ignition meansaccommodating chamber 23 and the combustion chamber 22 can be incommunication with each other through the flame-transferring hole 26.

A substantially cylindrical coolant 7 having a small difference ofdensity in the axial direction is disposed so as to surround the outerperiphery of the combustion chamber 22 storing the gas generating agent6. The coolant 7 is for purifying and/or cooling a combustion gasgenerated due to combustion of the gas generating agent 6. The coolant 7is formed by compressing, at least in the axial direction, the upper andlower opposite ends of the molded product made of wire rods.

Particularly, in the inflator shown in the present embodiment, theinternal pressure at the time of combustion of the gas generating agent6 in the housing 3 is adjusted by the total sum of the opening areas(“the total opening area” hereinafter) of all the gas discharge ports 11formed in the diffuser shell 1. Accordingly, a pressure loss of thecoolant 7 in the radial direction is set smaller than a pressure loss ofall gas discharge ports 11.

The coolant 7 is held between the diffuser shell 1 and the closure shell2 by welding the both shells with each other. In the present embodiment,a short pass preventing means 51 which covers the inner peripheralsurface of the coolant 7 on the diffuser shell 1 side is interposedbetween a coolant 7 end surface and a ceiling inner surface 29 of thediffuser shell 1 so as to prevent the combustion gas from passingbetween the coolant 7 end surface and the ceiling inner surface 29 ofthe diffuser shell 1. The short pass preventing means 51 is integrallyformed with a flame-repellent plate 50 for protecting the coolant from aflame of the transfer charge discharged from the flame-transferringhole. This flame-repellent plate 50 may be formed as a separate memberfrom the short pass preventing means 51, or a perforated basket formedat the specified area with a plurality of through holes may be usedinstead of the flame-repellent plate 50. A gap 9 is secured outside thecoolant 7 so that the combustion gas can pass through the entire surfaceof the coolant 7.

The gas discharge ports 11 formed in the diffuser shell 1 are closed bya seal tape 25 to block entering of the air. The seal tape 25 isruptured when the gas is discharged. This seal tape 25 is for protectingthe gas generating agent from the outside moisture, and has no effect onadjusting of performance such as combustion internal pressure.

In the inflator constructed in the above-described manner, the electricignition type ignition means 4 is activated by an activation signaloutputted from the sensor detecting an impact to ignite and burn thetransfer charge 5. A flame of the burnt transfer charge 5 is dischargedfrom the flame-transferring hole 26 of the inner cylinder member 13 intothe combustion chamber 22, and then ignites and burns the gas generatingagent 6 in the combustion chamber 22. By the combustion of the gasgenerating agent 6, a large amount of combustion gas is generated. Thecombustion gas is cooled while the gas passes through the coolant 7, thecombustion residues in the gas are collected, and then, the gas rupturesthe seal tape 25 and is discharged from the gas discharge ports 11. Whenthe combustion gas passes through the coolant 7, the combustion gas canbe purified and cooled, using the entire surface of the coolant 7because of the gap 9 secured on the outer periphery of the coolant 7.However, if a portion (the upper portion) of the inner peripheralsurface of the coolant 7 is covered with the flame-repellent plate asshown in this embodiment, or is covered with the upper portion of theperforated basket, the combustion gas generated due to combustion of thegas generating agent 6 cannot pass through the covered portion, nor thegas cannot be cooled or purified properly. Therefore, if a coolant,which has an uneven density with a higher density portion and a lowerdensity portion in the axial direction because of the compression mannersuch as the conventional coolant, is used, the output performance of theinflator is varied depending upon which portion between a higher densityportion and a lower density portion is covered. However, if the unevendensity in the axial direction is small such as the coolant 7 of thepresent invention, a stable operational output can be obtained even ifwhich one of the ends comes closer to the housing. Further, the coolantdoes not need a disposing direction, and there is no effect on theoperational performance even if which one of the ends comes closer tothe housing. Thus, it is unnecessary to arrange the disposing directionwhen the coolant is assembled into the inflator, and productivity can beimproved.

FIG. 8 is a longitudinal sectional view showing another embodiment ofthe inflator for air bag according to the present invention. Thisinflator has a structure particularly suitable for disposing on anpassenger side.

The inflator shown in this drawing uses a cylindrical housing 103 havingan axial length longer than outer most diameter. An inner space of thehousing 103 is divided into a combustion chamber 122 storing a gasgenerating agent 106 and a coolant accommodating chamber 130accommodating a coolant 107. Both the chambers are conjoined with eachother in the axial direction. In the portion of a peripheral wall of thehousing 103 where the coolant accommodating chamber 130 is provided, aplurality of gas discharge ports 111 are formed. The gas discharge ports111 are closed by seal tapes 125 for moisture-proof inside the housing103.

In addition to the gas generating agent 106, ignition means, whichincludes an electric ignition type ignition means 104 to be activatedupon an impact and an transfer charge 105 which is to be ignited andburnt upon activation of the ignition means 104 for generating a flame,is disposed in the combustion chamber 122. In FIG. 4, the ignition meansis formed as a structure comprising an initiator collar 114 fixed on theend surface of the housing, an ignition means 104 secured to theinitiator collar 114, an transfer charge 105 disposed adjacent to theignition means 104, and a cylindrical container 131 surrounding thetransfer charge 105 and being fixed to the initiator collar 114.

The coolant 107 disposed in the coolant accommodating chamber 130 is forpurifying and/or cooling a combustion gas generated in the combustionchamber 122, and a coolant which is formed in the same manner as that ofthe Embodiment 1, with a small density-difference in the axial directionis used. The coolant 107 is cylindrical in shape, and an end thereof onthe combustion chamber 122 side is supported by a coolant supportingmember 132, and the coolant 107 is disposed coaxially with the housing103 and facing the inner peripheral surface of the housing 103. A gap109 having a predetermined width and functioning as a gas passage isprovided between the outer peripheral surface of the coolant 107 and aninner peripheral surface of the housing 103. In the present embodiment,the coolant supporting member 132 is formed by providing peripheralwalls on the inner periphery and the outer periphery of an annularportion 133 having substantially the same shape as an end of the coolant107. The inner periphery of the coolant 107 is supported by a peripheralwall 134 of the inner peripheral side, and a peripheral wall 135 of theouter peripheral side is held by the inner peripheral surface of thehousing 103.

A sectioning member 136, which divides the combustion chamber 122 andthe coolant accommodating chamber 130, comprises a circular portion 137closing the housing in the radial direction, and a peripheral wall 138integrally formed with a peripheral edge of the circular portion 137.The circular portion 137 is provided with a communication hole 145 forcommunicating both chambers. A combustion gas generated in thecombustion chamber 122 reaches the coolant accommodating chamber 130through the communication hole 145. In the present embodiment, thesectioning member 136 is provided with a communication hole 145 havingsubstantially the same size as an inner diameter of the coolant 107. Awire mesh 139 is disposed on the communication hole 145 so that the gasgenerating agent 106 in the combustion chamber 122 should not move intothe coolant accommodating chamber 130 at the time of combustion. Anykind of wire mesh may be used as the wire mesh 139 as long as a size ofmesh is good enough to block movement of the gas generating agent 106during combustion, not having a ventilation resistance such as tocontrol the combustion performance. Of course, an expanded metal can beused instead of the wire mesh.

In the inflator in the present embodiment, the transfer charge 105 isburnt by activation of the ignitor 104 due to an activation signaltransmitted from an impact sensor or the like which detects an impact,and the flame thereof ejects from the flame-transferring hole 126 formedin the cylindrical container 131 to ignite and burn the gas generatingagent 106. A combustion gas generated by the combustion of the gasgenerating agent 106 flows into the coolant accommodating chamber 130through the communication hole 145 of a partition wall 136. Thecombustion gas passes through the entire surface of the coolant 107 andis purified and cooled, and then ruptures the seal tapes 125 and isdischarged from the gas discharge ports 111.

In FIG. 8, the numeral 140 designates a stud bolt for mounting theinflator to a module case.

“Embodiment of Air Bag Apparatus”

FIG. 9 shows an embodiment of an air bag apparatus of the presentinvention provided with an inflator using an electric ignition typeignition means.

This air bag apparatus comprises an inflator 200, an impact sensor 201,a control unit 202, a module case 203 and an air bag 204.

As the inflator 200, the inflator explained based on FIG. 1 is used, andits activation performance is adjusted to give an occupant as a smallimpact as possible at the initial activation process of the inflator.

The impact sensor 201 can comprise a semiconductor type accelerationsensor for example. In the semiconductor type acceleration sensor, foursemiconductor strain gauges are formed on a beam of a silicon substratedesigned to bend when acceleration is applied, and these semiconductorstrain gauges are bridge-connected. When the acceleration is applied,the beam is bent, and strain is generated on its surface. The resistanceof the semiconductor strain gauge is changed due to this strain, and thechange in resistance is detected as a voltage signal in proportion tothe acceleration.

The control unit 202 includes an ignition judging circuit to which asignal from the semiconductor type acceleration sensor is inputted. Thecontrol unit 202 starts calculation when the impact signal from thesensor 201 exceeds a certain value, and when the calculated resultexceeds a certain value, the control unit outputs an activation signalto the ignition means 4 of the inflator 200.

The module case 203 is formed of polyurethane for example, and includesa module cover 205. The air bag 204 and the inflator 200 areaccommodated in the module case 203, thereby forming a pad module. Whenthe pad module is mounted on the driver side of an automobile, the padmodule is usually mounted to a steering wheel 207.

The air bag 204 is formed of nylon (e.g., nylon 66) or polyester, itsbag opening 206 surrounds the gas discharge port of the inflator, andthe air bag 204 is fixed to a flange of the inflator in a folded state.

When the semiconductor type acceleration sensor 201 senses an impact atthe time of collision of an automobile, its signal is sent to thecontrol unit 202, and when the impact signal from the sensor exceeds thecertain value, the control unit 202 starts calculation. When thecalculated result exceeds the certain value, the control unit outputs anactivation signal to the ignition means 4 of the inflator 200. With thisactivation, ignition means (12 a, 12 b) are activated to ignite the gasgenerating agent, and the gas generated agent is burnt to generate agas. This gas is ejected into the air bag 204, thereby allowing the airbag to break the module cover 205 and inflating to form a cushion forabsorbing an impact between the steering wheel 207 and the occupant.

1. A coolant for an air bag inflator, comprising: a cylindrical coolantbody having a uniform thickness defined by an outer diameter and aninner diameter thereof and adapted to be disposed in a housing of theinflator for at least one of cooling and purifying gas discharged fromthe inflator, said coolant being formed by compressing a first end of amolded product made of wire rods in an axial direction thereof, andcompressing a second end, opposing the first end, of the molded productalong the axial direction, such that an absolute value of a differencebetween a radial pressure loss of the axially upper half portion of saidcoolant closer to the first end and a radial pressure loss of theaxially lower half portion of said coolant closer to the second end isadjusted to be 10 mmH₂O or less at a flow rate of 250 liters/minuteunder the atmosphere of 20° C.
 2. A coolant for an air bag inflatoraccording to claim 1, wherein the absolute value is 6 mmH₂O or less at aflow rate of 250 liters/minute under the atmosphere of 20° C.
 3. Acoolant for an air bag inflator according to claim 1, a difference inpressure losses between a vicinity of the first end and a vicinity ofthe second end of said coolant is 10 mmH₂O or less, when it is measuredin accordance with the following method: 1) covering an inner peripheralsurface of a cylindrically formed coolant from one of its axial end toits one-half the height with an annular covering member; 2) closing oneof the first end and the second end of said coolant, in which thecovering member is fitted, with a first supporting member having amanometer, closing the other of the first end and the second end of saidcoolant with a second supporting member having a gas-inflow pipe and agas-flow meter, and fixing said coolant axially to prevent air fromleaking between ends of said coolant and the supporting members; 3)introducing the air at a flow rate of 250 liters/minute from thegas-inflow pipe into an inner space of the covering member under theatmosphere of 20° C., and the pressure loss is measured; 4) turning saidcoolant the other way round with respect to the axial direction andcovering the inner peripheral surface of a cylindrically formed coolantfrom the other one of its axial end to its one-half the height with theannular covering member; 5) closing the other of the first end and thesecond end of said coolant, in which the covering member is fitted, withthe first supporting member, closing the one of the first end and thesecond end of said coolant with the second supporting member, and fixingsaid coolant axially to prevent air from leaking between ends of saidcoolant and the supporting members; 6) introducing the air at a flowrate of 250 liters/minute from the gas-inflow pipe into an inner spaceof the covering member under the atmosphere of 20° C., and measuring thepressure loss and 7) obtaining a difference in the pressure loss valuesobtained in 3) and 6), and determining its absolute value as adifference in radial pressure losses in the axial ends of said coolant.4. A coolant for an air bag inflator according to claim 1, wherein abulk density of said coolant is 3.0 to 5.0 g/cm³, and said coolant has apressure loss of 10 mmH₂O to 2000 mmH₂O with respect to an amount of airof 1000 liters minute⁻¹ under the atmosphere of 20° C.
 5. A coolant foran air bag inflator according to claim 1, wherein said coolant is anannular laminated body made of wire mesh formed by knittingstainless-steel wire rods.
 6. A method of producing a coolant for an airbag inflator, comprising: compressing a first end of a cylindricalmolded product having a uniform thickness defined by an outer diameterand an inner diameter thereof in an axial direction thereof; andcompressing a second end of the cylindrical molded product in the axialdirection, such that an absolute value of a difference between a radialpressure loss of the axially upper half portion of the molded productcloser to the first end and a radial pressure loss of the axially lowerhalf portion of the molded product closer to the second end is adjustedto be 10 mmH₂O or less at a flow rate of 250 liters/minute under theatmosphere of 20° C.
 7. The method of producing a coolant according toclaim 6, further comprising: adjusting a difference in pressure lossesbetween axially opposite ends of the molded product to be 10 mmH₂O orless when it is measured in accordance with the following method: 1)covering an inner peripheral surface of a cylindrically formed coolantfrom one of its axial end to its one-half the height with an annularcovering member; 2) closing one of the first end and the second end ofsaid coolant, in which the covering member is fitted, with a firstsupporting member having a manometer, closing the other of the first endand the second end of said coolant with a second supporting memberhaving a gas-inflow pipe and a gas-flow meter, and axially fixing saidcoolant to prevent air from leaking between ends of said coolant and thesupporting members; 3) introducing the air at a flow rate of 250liters/minute from the gas-inflow pipe into an inner space of thecovering member under the atmosphere of 20° C., and the pressure loss ismeasured; 4) turning said coolant the other way round with respect tothe axial direction and covering the inner peripheral surface of acylindrically formed coolant from the other one of its axial end to itsone-half the height with the annular covering member; 5) closing theother of the first end and the second end of said coolant, in which thecovering member is fitted, with the first supporting member, closing theone of the first end and the second end of said coolant with the secondsupporting member, and fixing said coolant axially to prevent air fromleaking between ends of said coolant and the supporting members; 6)introducing the air at a flow rate of 250 liters/minute from thegas-inflow pipe into an inner space of the covering member under theatmosphere of 20° C., and measuring the pressure loss and 7) obtaining adifference in the pressure-loss values obtained in 3) and 6), anddetermining its absolute value as a difference in radial pressure lossesin the axial ends of said coolant.
 8. The method of producing a coolantaccording to claims 6 or 7, wherein said compressing steps include, thefirst compression step of compressing a first end of the molded productin its axial direction, and the second compression step of turning themolded product axially upside down and further compressing a second endof the molded product in the axial direction.
 9. The method of producinga coolant according claim 8, wherein compressing distances in the firstand second compression steps are substantially equal.
 10. The method ofproducing a coolant according to claim 6, further comprising:compressing the molded product in a the radial direction thereof.
 11. Amethod of producing a coolant according to claim 6, wherein said moldedproduct is an annular laminated body obtained by forming a knitted wiremesh made of stainless-steel wire rods into a cylindrical body, pressingthe cylindrical body in the radial direction to form into a plate body,and then rolling said plate body many times cylindrically.
 12. An airbag inflator, comprising: a housing having a gas discharge port;ignition means adapted to be activated upon an impact; gas generatingmeans adapted to be ignited and burnt due to activation of the ignitionmeans for generating a combustion gas; and coolant means for one ofpurifying and cooling said combustion gas, said coolant means being thecoolant means according to claim
 1. 13. An air bag apparatus,comprising: an air bad inflator; an impact sensor for detecting animpact to activate said inflator; an air bag introducing therein a gasgenerated by said inflator to inflate; and a module case foraccommodating said air bag, wherein said air bag inflator is theinflator according to claim 12.